This application pertains to the art of mechanism actuators and more particularly to rotary actuators.
The invention is particularly applicable to a rotary actuator for use in controlling fluid flow through valves and the like and will be described with particular reference thereto; however, it will be appreciated by those skilled in the art that the invention has broader applications and may be employed in other environments where rotary movement is desired and/or necessary for purposes of controlling operation of any mechanism.
Many types of rotary actuators of the rack and pinion type are known in the art and many of them have been developed for specific control applications. However, virtually all of these prior actuators have had complex constructions or have been comprised of a substantial number of components so that during assembly thereof there was undesired tolerance build-ups or stacking in the final actuator assembly. Even those prior actuators which contemplated simpler designs still were constructed in such a manner that tolerance stacking was present. While such a condition may not cause difficulty where the control limitations of the actuator are not important or critical, tolerance build-ups are extremely undesirable and unacceptable in those instances where the actuator will be employed for providing very precise rotary control between closely defined limits for mechanisms such as, for example, valves or the like and automated instruments such as chromatographs and analysers.
Another problem which has been present in prior actuators is the nature and/or lack of support for the elongated rack member which is employed to impart rotational movement to a pinion for purposes of converting linear movement to rotational movement. Here, again, where precise control is not a factor, the lack of such locating and support means is not particularly significant although wear and premature failure of the apparatus between the rack and pinion may result. However, the improperly designed locating and support means, or the lack thereof altogether, can cause overall operational difficulties as well as imprecise operation.
Two prior patents which disclose structures that typically demonstrate the foregoing problems are the Heese, U.S. Pat. No. 3,494,205 and Van Sittert, U.S. Pat. No. 2,224,708 patents. By virtue of the sheer number of components in Heese, tolerance build-ups will occur between the components so that a precise control function when using the actuator disclosed by this patent is not possible. Also, there is no means provided for positively locating and supporting the rack in the Heese type actuator. Thus, it is possible for the rack to rotate slightly relative to the pinion and cause premature wear or failure between these two components. Van Sittert also discloses a structure where tolerance build-ups will occur. Likewise, the rack locating and supporting structure is such that only minimal support is provided for the rack. Again, these structural deficiencies are unacceptable for actuators of the type required for providing precise rotary control between predetermined close limits.
Another area of objection to prior rotary actuators is the fact that many of them merely facilitate control of a single mechanism through means of a single ended operating member. Oftentimes, it is desirable to control at least a pair of mechanisms by means of a single actuator, particularly in a complex system control environment where, for example, a plurality of valves or the like are employed in a system for controlling fluid flow.
Another deficiency in prior rotary actuator designs relates to the means provided for mounting mechanisms to the actuators themselves. For those environments where precision rotary control is required, it is imperative that the mechanisms be precisely located relative to the actuator in order that proper and desired rotary control may be realized. Prior actuators have not addressed themselves to the provision of convenient means to meet this need.
The present invention contemplates a new and improved apparatus which overcomes these problems and others, and provides a new and improved rotary actuator which is simple in design, economical to manufacture, provides precise rotary movement between closely defined limits and is readily adaptable to use in any number of environments for controlling various types of mechanisms.